Implant with patient-specific porous structure

ABSTRACT

A method of manufacturing a joint implant for a joint of a specific patient includes obtaining a three-dimensional image of a bone of the joint of the specific patient from medical imaging scans of the bone of the patient and determining on the three-dimensional image a resection plane for contacting a corresponding planar surface of the joint implant for the specific patient. The method includes determining a three-dimensional image of a porous structure of a bone layer along the resection plane from the medical imaging scans of the patient. The joint implant is manufactured with a layer of a patient-specific porous construct attached to the planar surface of the joint implant. The layer of the patient-specific porous construct substantially replicates the porous structure of the bone layer of the specific patient.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of U.S. Provisional Patent Application No. 61/594,100 filed on Feb. 2, 2012. The entire disclosure of the above application is incorporated herein by reference.

FIELD

This application is directed to orthopedic implants having a patient-specific porous structure.

INTRODUCTION

The present teachings provide various orthopedic implants for joint arthroplasty, such as knee arthroplasty. The implants are designed and constructed based on three-dimensional digital images of the patient's joint. The digital images of the patient's joint can be reconstructed from medical scans, such as MRI, CT or X-ray or other imaging scans of the patient using commercially available CAD (Computer Aided Design) and/or other imaging software.

According to the present teachings, the porous structure of the bone of a joint of a specific patient can be determined from the imaging scans of the patient's joint along preoperatively planned resections or other implant engagement surfaces. Custom implants for the patient can be designed and manufactured to have a patient-specific porous structure that matches as a mirror surface the patient's porous structure along corresponding surfaces of engagement between the implant and the bone of the joint of the patient.

SUMMARY

The present teachings provide a method of manufacturing a joint implant for a joint of a specific patient includes obtaining a three-dimensional image of a bone of the joint of the specific patient from medical imaging scans of the bone of the patient and determining on the three-dimensional image a resection plane for contacting a corresponding planar surface of the joint implant for the specific patient. The method includes determining a three-dimensional image of a porous structure of a bone layer along the resection plane from the medical imaging scans of the patient. The joint implant is manufactured with a layer of a patient-specific porous construct attached to the planar surface of the joint implant. The layer of the patient-specific porous construct substantially replicates the porous structure of the bone layer of the specific patient.

The present teachings also provide an orthopedic implant. The orthopedic implant can be a femoral knee implant. The femoral knee implant can include a femoral knee implant core having an interior multiplanar surface including a plurality of a planar surfaces configured to correspond to a plurality of corresponding resection planes of a distal femoral bone of the specific patient. The femoral knee implant can also include a patient-specific porous construct including a plurality of layers attached to corresponding planar surfaces of the femoral knee implant. Each layer is constructed to replicate a three-dimensional porous structure of a bone layer along a corresponding resection plane of femoral bone. The porous structure of the bone layer is determined from medical imaging scans of the un-resected femoral bone.

The orthopedic implant can be a tibial knee implant having a distal surface configured to correspond to a resection plane of a tibial bone of the specific patient and including a patient-specific porous construct. The patient-specific porous construct includes a layer attached to the distal surface of the tibial knee implant. The layer is constructed to replicate a three-dimensional porous structure of a bone layer along the resection plane of tibial bone. The porous structure of the bone layer is determined from medical imaging scans of the un-resected tibial bone.

Further areas of applicability of the present teachings will become apparent from the description provided hereinafter. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present teachings.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure.

FIG. 1 is a digital three-dimensional image of a patient's femoral bone reconstructed from image scans of the patient and displayed on an electronic screen according to the present teachings;

FIG. 2 is a digital three-dimensional image of a patient's tibial bone reconstructed from image scans of the patient and displayed on an electronic screen according to the present teachings;

FIG. 3 is a sectional view of an exemplary femoral implant having a bone-engagement layer or surface with a patient-specific porous structure designed and constructed to match the porous structure of the femoral bone of the patient along corresponding surfaces or layers according to the present teachings;

FIG. 4 is a back view of the femoral implant of FIG. 3 illustrating different porous structures of the bone engagement surface of the femoral implant according to the present teachings;

FIG. 5 is a digital three-dimensional image of a patient's femoral bone illustrating planned bone resection surfaces corresponding to the bone engagement surface of FIG. 3 for matching porous structures according to the present teachings;

FIG. 6 is a three dimensional patient-specific porous construct for the bone engagement surface of FIG. 3 and matching the porous structure along the corresponding surfaces of the femoral bone according to the present teachings;

FIG. 6A is a three-dimensional image reconstructed from micro-CT scanner showing a detail of a porous structure of a bone;

FIG. 7 is a top isometric view of an exemplary tibial tray according to the present teachings;

FIG. 8 is a bottom isometric view of the tibial tray of FIG. 7; and

FIG. 9 is bottom view of a tibial tray showing representative areas of different porous structures matching corresponding porous structures of the tibial bone of the patient according to the present teachings.

Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.

DESCRIPTION OF VARIOUS EMBODIMENTS

The following description is merely exemplary in nature and is in no way intended to limit the present teachings, applications, or uses. For example, although some of the present teachings are illustrated for implants for a knee joint, the present teachings can be used for implants of any other joint of the patient, including hip joint, shoulder joint, ankle joint, etc.

The present teachings provide custom-made implants and associated manufacturing methods for a specific-patient. Each custom-made implant has a bone-engagement surface (or surfaces) with a porous layer or porous construct attached thereon. The porous construct has a patient-specific porous structure, i.e. a porous structure that matches the three-dimensional porous structure of the bone of the patient along corresponding surface (or surfaces) and through a specified thickness, forming a patient-specific porous layer. The porous structure, as used herein, includes the size, shape, and distribution of pores and varies depending on location in the bone. The porous structure of the bone of the patient along particular surfaces (and extending through a specified thickness as a layer) that will engage the implant can be determined by imaging the bone of the patient using imaging scans, such as CT or MRI. The porous structure can be distinguished from a single porosity value that can be an average, mean, median, or volumetric measure, such as ratio of a volume of interstices or pores of the bone over a volume of the mass of the bone.

The porous structure can be obtained from three-dimensional images of the patient's bone reconstructed from MRI or CT scans of the patient using scanners of adequate or desired resolution depending on the imaged anatomy of the patient. For example, commercially available high resolution CT or MRI scanners can be used (hrCT or hrMRI scanners) or even micro-CT scanners (μCT scanners) with voxel resolution of the order of a few microns (μm) including, for example, 20 μm, 40 μm or other size.

Porous structure determination and three-dimensional reconstruction of bone images from two-dimensional CT or MRI or μCT image data can be obtained using, for example, commercially available software from Materialise USA, Plymouth, Mich., such as the Mimics© Innovation Suite or other vendors. For example, medical imaging data from CT, or MRI or μCT scanners can be segmented to create accurate, patient-specific three-dimensional models in “STL” or other similar format files. The STL file format is native to stereolithography CAD (Computer Aided Design) software and can be used for rapid prototyping and computer-aided manufacturing. A related file format is AMF (Additive Manufacturing File Format), which can support color and multiple materials. The STL or AMF files can be also converted to IGES (Initial Graphics Exchange Specification) files or other similar format files that are neutral data formats and allow this digital exchange of information among different CAD software systems. For example, these digital files can be used with various commercially-available CAD software packages for designing custom and non-custom implants and/or instruments and for planning surgical procedures.

More specifically, using the above methods, the implants of the present teachings can be designed and manufactured to incorporate a patient-specific porous construct that matches identically (as a mirror image or negative or inverse layer) the porous structure of the bone at some or all of the bone layers that contact and engage the implant, such that the porous structure of the implant is a seamless continuation of the porous structure of the bone along the surfaces of contact between the implant and the bone. The patient-specific porous construct can be manufactured by additive manufacturing technology using instructions based on the medical imaging files either directly on the implant or separately and subsequently attached to the implant or in one integrated manufacturing procedure.

Generally, in the preoperative planning stage for arthroplasty, imaging data of the relevant anatomy of a patient can be obtained at a medical facility or doctor's office, using one or more of medical imaging methods described above. The imaging data can include various medical scans of a relevant portion of the patient's anatomy, as needed for joint modeling. For knee joint arthroplasty, images of all the knee joint and, optionally, images of the femoral head or hip joint and ankle joint for mechanical axis determination can be taken. An initial preoperative plan can be prepared for the patient in image space and can include planning and determination for joint resections for receiving corresponding implants, custom implant design or non-custom implant selection, sizing and fitting and designing patient-specific alignment and/or resection guides and other instruments for guiding the joint resections, drilling holes for locating pins or other fasteners and for other guidance during the surgical procedure.

The patient-specific porous structures for the implants of the present teachings can manufactured by casting, welding, laser cutting, molding or various stereolithography methods, such as, for example, selective laser sintering, fused deposition modeling or other rapid prototyping methods. In some embodiments, the non-porous core of the implant can be made of a biocompatible metal or alloy, such as titanium, and the patient-specific porous construct can include, for example, porous titanium, such as the Regenerex© porous titanium material available from Biomet Manufacturing Corp., Warsaw, Ind., USA. Exemplary method for creating porous metal constructs are described in commonly assigned patent application “Method and Apparatus for Use of Porous Implants”, Ser. No. 11/294,692, filed Dec. 5, 2005 and currently published as US 2006/0241775, the disclosure of which is incorporated herein by reference.

Referring to FIGS. 1 and 2, three-dimensional images of bones reconstructed from medical scans of a specific patient by the imaging and CAD software discussed above are illustrated generically. The bone images are shown displayed on an electronic screen 52 of a computer 50, such as, for example a desktop, laptop, smartphone, tablet, terminal or other processor communication with an electronic screen 52. In FIG. 1, the bone image 70 is illustrated as an image of distal femoral bone 70. In FIG. 2, the bone image 90 is illustrated as a proximal tibial bone.

Referring to FIGS. 3-6, the present teachings are illustrated for a femoral knee implant 100. The femoral knee implant 100 includes an implant core 103 and a patient-specific porous construct 101. The implant core 103 can be non-porous metal or alloy. The implant core 103 has an outer (exterior) articulating surface 102 that faces the patient's knee joint for articulation with the patient's natural tibia or a prosthetic tibial component. Opposite to the articulating surface 102, the implant 100 has an inner bone engagement surface formed by the patient-specific porous construct 101. In the exemplary embodiment of FIG. 2, the implant 100 engages the patient's femoral bone along a multi-planar surface, specifically along a plurality of pre-planned planar resection planes, as illustrated in the bone image 70 in FIG. 5, in which the images of five resection planes 74, 76, 78, 80 and 82 are shown. The patient-specific porous construct 101 includes a corresponding multiplanar bone engagement surface, including planar surfaces 124 (124 a, 124 b in FIG. 6), 126, 128, 130, 132. The corresponding opposite surfaces of the patient-specific porous construct 101 are attached and coincide to corresponding inner surfaces 104, 106, 18, 110 and 112 of the implant core 103. In knee implant terminology, resection plane 74 corresponds to a posterior resection, resection plane 76 to a chamfer posterior resection, resection plane 78 to a distal resection, resection plane 80 to a chamfer anterior resection, and resection plane 82 to an anterior resection. The corresponding surfaces of the implant core 103 and the porous construct can be similarly referenced as posterior (104, 124), posterior chamfer (106, 126), distal (108, 128), anterior chamfer (110, 130) and anterior (122, 132) flanges or planes. The porous construct 101 matches the porous structure of the bone along corresponding layers of thickness “t” as shown in FIGS. 5 and 6.

It will be appreciated that the porous structure of the patient-specific porous construct 101 can vary from flange to flange and within a flange, in addition to varying through the thickness of the flange. For example, in the schematic illustration of FIG. 4, different medial and lateral distal porous structures 138 a, 138 b (corresponding to flange 128 of the patient-specific porous construct 101 shown in FIG. 3), and different medial and lateral chamfer posterior porous structure 136 a, 136 b (corresponding to flange 126 of the patient-specific porous construct 101 shown in FIG. 3) are indicated schematically. Further, the porous structure can vary within each planar section in a patient-specific manner. For example, the anterior chamfer porous structure 140 (corresponding to flange 130 of the patient-specific porous construct 101 shown in FIG. 3) can decrease or increase along a medial-lateral direction (arrow A), although it can also vary nonlinearly, non-monotonically or otherwise for a specific patient.

In the exemplary embodiments of FIGS. 1-6, the patient-specific porous construct 101 for the femoral knee implant 100 replicates point-by-point the three-dimensional porous structure of the distal femur of a specific patient over a layer of thickness t along the planned resection planes 74, 76, 78, 80 and 82, as obtained from micro-CT scans of the specific patient or from other medical imaging scans of sufficiently high resolution (hrCT or hrMRI) to show the porous structure of the bone. In this example, the resection planes 74, 76, 78, 80 and 82 may be mostly located various grades cancellous bone, although some cortical bone may be involved in some edge locations. Accordingly, the patient-specific three-dimensional porous construct 101 replicates as a mirror structure and congruently continues the variable porous structure of a layer of cancellous (and possibly cortical) bone that is uniquely associated with the specific patient. A detail of the three-dimensional porous structure of a layer of bone is illustrated in FIG. 6A which shows a three-dimensional image of a bone layer reconstructed from a two-dimensional CT slices using a commercially available micro-CT scanner, as discussed above. The resolution or voxel size used for the image of FIG. 6A is about 20 μm.

Referring to FIGS. 7-9, the present teachings are illustrated for a tibial implant 200. The tibial implant 200 is, for example, a tibial tray having a proximal surface 202 facing the knee joint of the patient and an opposite distal surface 204 on which a patient-specific three-dimensional porous construct 220 is attached. The tibial implant 200 can include various anchoring members for engaging the patient's tibial bone. In the exemplary embodiment of FIGS. 7 and 8, the anchoring members include four peripheral pegs 208 configured to engage firm cancellous bone. The peripheral pegs 208 are made of non-porous metal and include a square body terminating at a pyramidal (pointed) tip for insertion and anchoring into the cancellous bone. The anchoring members can also include a central stem 206. In the embodiment of FIG. 8, the central stem 206 is tapered, splined and made of non-porous metal. Accordingly, the patient-specific porous construct 220 does not extend to the areas of the distal surface 204 of the tibial implant that correspond to the footprints of the peripheral pegs 208 and central stem 206. The tibial implant 200 can include one or more anterior locking tabs 205 and/or posterior locking tab 207 for engaging corresponding grooves of a tibial bearing.

FIG. 9 illustrates diagrammatically regions of different porous structures corresponding to the patient's proximal tibia along a resection plane for receiving the tibial implant 200. For example, a peripheral annular region 232 replicates the porous structure of the patient's proximal tibial cortical bone. Additionally, regions of anterior, posterior and medial and lateral different porous structures 226, 228, 224 and 230 replicating corresponding tibial bone porous structures are illustrated. Further, the porous structure within a region may not be uniform or homogeneous. For example, a local porous structure 226 may be surrounded by a region of different porous structure 224. It should also be noted that the porous structure of the areas of the proximal tibia corresponding to the footprints of the peripheral pegs 206 and the central stem will not be replicated in the patient-specific porous construct 220.

Example embodiments are provided so that this disclosure is thorough, and fully conveys the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure.

It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail. Accordingly, individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same embodiment may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure. 

What is claimed is:
 1. A method of manufacturing a joint implant for a joint of a specific patient comprising: obtaining a three-dimensional image of a bone of the joint of the specific patient from medical imaging scans of the bone of the patient; determining on the three-dimensional image a resection plane for contacting a corresponding planar surface of the joint implant for the specific patient; determining a three-dimensional image of a porous structure of a bone layer along the resection plane from the medical imaging scans of the patient; and manufacturing the joint implant with a layer of a patient-specific porous construct attached to the planar surface of the joint implant, the layer of the patient-specific porous construct being an inverse of the porous structure of the bone layer of the specific patient, such that the patient-specific porous construct mirrors the porous structure of the bone layer along the resection plane.
 2. The method of claim 1, wherein the joint implant is a femoral knee implant.
 3. The method of claim 2, wherein the planar surface of the joint implant is one of posterior, posterior chamfer, distal, anterior chamfer and anterior flange surface and wherein the layer of a patient-specific porous construct includes a corresponding surface.
 4. The method of claim 2, wherein the planar surface of the joint implant includes posterior, posterior chamfer, distal, anterior chamfer and anterior flange surfaces and wherein the layer of a patient-specific porous construct includes corresponding surfaces.
 5. The method of claim 1, wherein the porous construct includes porous metal.
 6. The method of claim 1, wherein the joint implant is a tibial knee implant.
 7. The method of claim 6, wherein the tibial knee implant is a tibial tray and the porous construct is attached to a distal surface of the tibial tray.
 8. The method of claim 7, wherein the tibial tray includes a plurality of anchoring members extending from the distal surface.
 9. The method of claim 8, wherein the porous construct excludes areas corresponding to footprints of the plurality of the anchoring members.
 10. The method of claim 1, further comprising manufacturing the patient-specific construct using additive manufacturing.
 11. The method of claim 1, wherein the resolution of the medical imaging scans is of the order of a few microns for voxel size.
 12. The method of claim 1, wherein the resolution of the medical imaging scans is about 20 microns of voxel size.
 13. A method of manufacturing a joint implant for a joint of a specific patient comprising: obtaining a three-dimensional image of a distal femoral bone of a joint of the specific patient from medical imaging scans of the distal femoral bone of the patient; determining on the three-dimensional image a plurality of resection planes for contacting corresponding planar surfaces of an implant core of the joint implant for the specific patient; determining a three-dimensional image of a porous structure of a bone layer along each of the corresponding resection planes from the medical imaging scans of the un-resected femoral bone of the patient; and manufacturing the joint implant with a plurality of layers of patient-specific porous constructs attached to the corresponding planar surfaces of the joint implant, each layer of the patient-specific porous construct being an inverse of the porous structure of the corresponding bone layer of the specific patient, such that each layer of the patient-specific porous construct mirrors the porous structure of the corresponding bone layer along the resection plane.
 14. The method of claim 13, wherein the plurality of planar surfaces includes five surfaces.
 15. The method of claim 13, wherein the plurality of planar surfaces includes posterior, anterior and distal surfaces.
 16. The method of claim 15, wherein the plurality of planar surfaces includes posterior chamfer and anterior chamfer surfaces.
 17. The method of claim 13, wherein the implant core includes non-porous material.
 18. The method of claim 13, wherein the implant core includes an exterior articulating surface.
 19. The method of claim 13, wherein the porous structure is determined from medical imaging scans with resolution of a few microns for voxel size.
 20. A method of manufacturing a joint implant for a joint of a specific patient comprising: obtaining a three-dimensional image of a tibial bone of the joint of the specific patient from medical imaging scans of the tibial bone of the patient; determining on the three-dimensional image a resection plane for contacting a corresponding planar surface of the joint implant for the specific patient; determining a three-dimensional image of a porous structure of a tibial bone layer along the resection plane from the medical imaging scans of the patient; and manufacturing the joint implant with a layer of a patient-specific porous construct attached to the planar surface of the joint implant, the layer of the patient-specific porous construct being an inverse of the porous structure of the tibial bone layer of the specific patient, such that the patient-specific porous construct mirrors the porous structure of the tibial bone layer along the resection plane.
 21. The method of claim 20, wherein the porous structure is determined from medical imaging scans with resolution of a few microns for voxel size.
 22. The method of claim 1, wherein the layer of the patient-specific porous construct being the inverse of the porous structure of the bone layer of the specific patient provides a seamless continuation of the porous structure of the bone along surfaces of contact between the implant and the bone.
 23. The method of claim 13, wherein each layer of the patient-specific porous construct being the inverse of the porous structure of the corresponding bone layer of the specific patient provides a seamless continuation of the porous structure of the bone along surfaces of contact between the implant and the bone.
 24. The method of claim 20, wherein the layer of the patient-specific porous construct being the inverse of the porous structure of the corresponding tibial bone layer of the specific patient provides a seamless continuation of the porous structure of the bone along surfaces of contact between the implant and the bone. 